1. Field of the Invention
This invention relates generally to methods and apparatus for identifying repetitively broadcast programs, and more particularly to a method and apparatus for identifying repetitively broadcast programs, such as commercial advertisements broadcast on television and radio.
2. Description of the Prior Art
Systems for identifying programs such as television and radio programs that are broadcast are known. Such systems fall into various categories. These categories include manual systems wherein a clerk keeps a log indicating the programs broadcast by a given station; systems that detect identifying signals present in the television or radio broadcast signal; and systems that monitor and analyze the program content of the broadcast signal utilizing pattern recognition and correlation techniques to identify the program. While all of these systems provide a way to identify programs and to confirm that commercial advertisements are made available for public viewing, the manual methods are slow in acquiring data and are prone to inaccuracies resulting from the entry of erroneous data that may be intentionally or unintentionally entered.
Systems that detect identification signals encoded on the broadcast signal require the cooperation of the broadcasters who must encode the programs prior to broadcast for such systems to be effective. Consequently, such systems are useable only on a limited number of broadcasts, such as network broadcasts. Other known systems monitor and analyze the content of the program itself, but heretofore the information processing requirements of such systems rendered such systems impractical or uneconomical because of the computing capacity required to analyze the vast quantity of information present in broadcast signals. Moreover, previous attempts to reduce the quantity of information processed tended to introduce inaccuracies.
An example of a system that utilizes the program content of a broadcast signal to identify the program is described in U.S. Pat. No. 3,919,479 to Moon et al. The Moon et al. system utilizes a non-linear analog transform to produce a low-frequency envelope waveform, and the information in the low-frequency envelope of predetermined time interval is digitized to generate a signature. The signatures thus generated are compared with reference signatures to identify the program. However, the Moon et al. system generates the signatures continuously, and consequently, requires a large computer to process the data thus generated.
Another system that monitors the program content of a broadcast signal is disclosed in U.S. Pat. No. 4,230,990 to Lert, Jr. et al. The system disclosed in Lert, Jr. et al. patent reduces the amount of data that must be processed, as compared to the data amount to be processed by the Moon et al. patent, by utilizing cues that are either externally generated or present in the program material to initiate the signature generation and correlation process only after a cue has been detected. However, in the system disclosed in the Lert, Jr. et al. patent, a signature is extracted at a predetermined time following a detected cue signal, and inaccuracies may be introduced if the signal is not stable at the time of signature extraction or the extracted signature must include a large quantity of data for identification of the program with the desired accuracy.